A fuel cell is a device that convers chemical energy into electrical energy. It is a clean energy source which allows for utilization of energy with high efficiency as compared to the existing internal-combustion engines and does not emit pollutants such as carbon dioxide, nitrogen oxides, sulfur oxides, etc. during the energy conversion process. In a fuel cell, a gaseous fuel such as hydrogen, etc. is supplied to an anode and a gaseous fuel such as oxygen, etc. is supplied to a cathode. At the anode, hydrogen is oxidized and electrons are released via an external circuit connected to the fuel cell. At the cathode, ions are generated as oxygen is reduced by the released electrons. The ions are delivered through a polymer electrolyte membrane present between the anode and the cathode. Electrical energy is produced as this process is repeated.
In order to overcome the low oxygen reduction reaction activity leading to high overvoltage at the cathode, platinum or a platinum-based catalyst having high activity is commonly used as an electrode catalyst in the existing fuel cell. At present, low-platinum or non-platinum catalysts are studied actively to overcome the high price and limited supply of Pt. In particular, for catalysts used in alkaline fuel cells, non-platinum transition metal catalysts and carbon-based catalysts are studied actively due to their high oxygen reduction reaction activity and durability.
The previous researches on non-platinum and carbon-based oxygen reduction catalysts have been mainly focused on binding with a heterogeneous element such as nitrogen, phosphorus, etc. to exhibit oxygen reduction activity. These non-platinum oxygen reduction catalysts have the problem of low durability after operation for a long time and the carbon-based catalysts are problematic in that heat treatment is necessary for binding with the heterogeneous element at high temperature and in that the quantity of the bound heterogeneous element is also limited. Accordingly, development of a catalyst which is capable of exhibiting high oxygen reduction reaction activity and durability without binding with a heterogeneous element is necessary.